Method for backing off broken studs



July 27, 1954 J. 0. HOOVER METHOD FOR BACKING OFF BROKEN STUDS Filed July 6, 1951 INVENTOR.

m e N E e W mm H w 0. W MVY M m Patented July 27, 1954 DEED 2 Claims.

This invention relates to a method for backing ofi broken studs.

In the backing off of broken studs, as heretofore proposed, a single round hole is first drilled in an end of the broken stud, and then a round extractor is inserted in such hole and rotary movement applied to the inserted extractor to effect the backing off of the stud. A round extractor in a round hole does not afford the proper gripping action for the backing off of the broken stud.

An object of the present invention is to provide a method for backing off broken studs which enables the formation of a hole in the broken stud of a type such as to insure a positive and proper gripping with a conformably shaped extractor when inserted therein.

Another object of the present invention is to provide a method for backing off broken studs which is simple in execution, and is positive in action.

Other objects of the present invention will become apparent from the following description taken in conjunction with the accompanying drawing, in which:

Figure l is a fragmentary sectional view showing a broken stud in threaded engagement with a casing.

Figure 2 shows a centering punch in position upon the end of the broken stud for forming the discernible points which serve as drilling axes for the respective overlapping holes.

Figure 3 shows the drill centered upon one of the formed discernible points and ready to drill into the end of the broken stud.

Figure 4 shows the completed hole formed in the end of the broken stud as the result of the drilling of the overlapping holes about each of the discernible points as the drilling axis.

Figure 5 shows the extractor in position in the completed hole formed in the end of the broken stud.

Figure 6 shows the extractor carrying the broken stud backed on of the casing.

Referring to Figure 1, the numeral 55 designates a broken stud which is in threaded engagement with the casing i i. In backing on or" such broken stud according to the method of the present invention there is formed simultaneously in an end of the broken stud three discernible points which are spaced equally from the center line of the stud and spaced from the perimeter of the stud. As shown in Figure 2, this formation is effected by placing a centering punch i2 which carries three centering points 43 spaced equally from each other upon the end it of the stud is so that the centering points are equally distant from the center line of the stud, and then applying an impactive force to the end of the punch of a magnitude such as to simultaneously impress upon the end of the broken stud three discernible points It, Figure 3, the latter points being likewise equally distant from each other and from the center line of the stud as well as being spaced from the perimeter of the stud.

With the completion of the three discernible points it: on the end Hi of the stud It, drilling in turn about each of such points as the drilling axis is caused to be done until three overlapping holes are formed of a depth to accommodate a conformably shaped extractor, the drilling being eifected by means of a drill it, Figure 3, whose radius is greater than the distance between each of the points 55 and the center line of the stud. Preferably, the drilling is effected by first centering the drill IS on one of the points is and causing the drill to penetrate to a depth of not more than one sixteenth of an inch, then repeating the centering and penetration of the drill in turn upon the other two of the points it, and these operations continued in turn upon the respective part formed holes until three overlapping holes of a depth sufficient to accommodate a conformably shaped extractor is attained. The resulting three overlapping holes form a single hole l'i, Figure 4, which is in the shape of a cloverleaf. While drilling the three overlapping holes it is advisable to angle the bit of the drill is slightly away from the center line of the stud. By so doing the centers of the individual holes will be preserved. and enable the holes to be drilled to any desired depth.

Inserted in the thus formed hole ll of the stud Iii is an extractor Iii, Figure 5, the extractor having the end 19 conformably shaped to fit such hole. With the extractor thus inserted, rotary movement is applied to the extractor in a direction such and for a time sufiicient to cause backing off of the broken stud it from the casing it as shown in Figure 6.

It is to be noted that since the drilled hole ll is sufliciently large to accommodate the triangular or conformably shaped tip of the extractor it it is unnecessary to drive the extractor into the hole. Therefore, no outward pressure is applied to the stud, causing expansion of the stud in the threads. Should the extractor be broken off in the hole in the stud removal of the broken tip can be accomplished easily, permitting the immediate insertion of another extractor. Should the broken stud in the casing prove too tight for the extractor there is nothing to interfere with the stud being drilled out completely and the hole retapped with an oversize thread,

I claim:

1. The method for backing ofi broken studs comprising forming simultaneously in an end of a broken stud three discernible points spaced equally from the center line of said stud and spaced from the perimeter of said stud, centering a drill whose radius is greater than the distance between each of said points and the center line of said stud upon one of said points, causing drilling of said drill about said one point as an axis to form part of a hole, centering said drill upon the other of said points, causing drilling of said drill about said other point as an axis to form a like part of another hole overlapping said first named hole, repeating the centering and drilling of said drill in turn upon said one and other points until completion of the formation of overlapping holes of a depth sufiicient to accommodate a conformably shaped extractor, inserting an extractor which is conformably shaped to fit the thus formed holes into said overlapping holes, and applying to said extractor rotary movement in the direction such as to cause backing off of said broken stud.

2. The method for backing off broken studs comprising impressing simultaneously in an end of a broken stud three discernible points spaced equally from the center line of said stud and spaced from the perimeter of the stud, drilling in turn about each of said points as an axis and With a drill Whose radius is greater than the distance between each of said points and the cen ter line of said stud to form overlapping holes of a depth sufiicient to accommodate a conformably shaped extractor, inserting an extractor which is conformably shaped to fit the thus formed holes into said overlapping holes, and applying to said extractor rotary movement in a direction such and for a time sufiicient to cause backing off of said broken stud.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,458,076 Potts June 5, 1923 1,547,944. Murphree July 28, 1925 2218,6955 Bradshaw July 8, 1941 2,397,216 Stellin Mar. 26, 19% 2,547,986 Van Dermark Apr. 10, 1951 FOREIGN PATENTS Number Country Date 5,170 Austria Sept. 10, 1901 372,994 Germany Apr. 6, 1923 581,942 Great Britain Oct. 30, 1946 954,633 France June 13, 1949 

